The present invention relates to a method to operate an opto-electronic sensor array and to such a sensor array.
The intrusion of objects into a monitored region is recognized, for example, by such sensor arrays, wherein an object recognition can also take place, in addition to a pure object detection signal, for example by a contour detection with a corresponding sensor selection. Conventional camera systems with CCD based solutions are frequently used as the sensor systems. These are, however, only conditionally usable in an industrial environment due to their high sensitivity to external light. Moreover, such CCD based solutions usually have too low a processing speed as typical image rates of only less than 30 Hz can be achieved with them.
It is an object of the invention to provide an opto-electronic sensor array and a method to operate such a sensor array in which an improved external light suppression, in particular an improved continuous light suppression, is possible. Furthermore, a higher processing speed than with CCD base solutions should be possible with this sensor array.
The object relating to the method to operate an opto-electronic sensor array in accordance with the invention is satisfied by a method in which a plurality of sequential operating light pulses are emitted into a monitored region, the operating light pulses reflected by an object in the monitored region are received by a spatially resolving receiver unit with a plurality of light-sensitive sensors, the light intensity of the respectively received reflected operating light pulses is in each case detected and stored synchronously with the emission of the operating light pulses during an activation interval and the light intensities stored for the sensors are transmitted after every activation interval in following transmission steps to a parallel processor with a plurality of parallel signal inputs for parallel signal processing, with the transmission in each transmission step taking place in each case for a plurality of sensors simultaneously.
The part of the object relating to the apparatus is satisfied by an opto-electronic sensor array comprising a light transmitter for the transmission of a plurality of sequential operating light pulses into a monitored region and a spatially resolving receiver unit comprising a plurality of light sensitive sensors for the reception of operating light pulses reflected from an object arranged in the monitored region, a synchronizing unit for the synchronization of the operating light pulses with an activation interval in which the sensors can each be activated to detect the light intensity of the reflected operating light pulses received in each case, a memory unit in which the light intensity detected during the activation interval for each sensor can be stored and a parallel processor comprising a plurality of signal inputs which is connected to corresponding outputs of the receiver unit for the parallel acceptance of a plurality of values of the light intensities stored in the memory unit.
In accordance with the invention, the light incident on the sensors is thus only evaluated for each sensor during sequential activation intervals and the corresponding light intensity is stored, for example, in the form of charges in a capacitor, with these activation intervals being synchronous to the emission of the operating light pulses so that the amount of the light reflected at the respective object plus the background light incident at this moment in time is stored as the light intensity. Background light outside the activation interval and thus present between the end of an operating light pulses and the beginning of the next operating light pulses is thus not stored in the receiver unit.
In connection with the transmission of the stored light intensities for a part of the sensors in each case in sequential transmission steps, it is thus prevented that during the transmission of the light intensities for a first part of the sensors in a first transmission step a constant integration of the background light incident on these sensors takes place, whereby a falsification of the evaluation signals would take place.
An improved non-sensitivity to external light over known sensor arrays is achieved in this way. Furthermore, a much higher processing speed is achieved in comparison with usual sensor arrays by the parallel transmission of a plurality of light intensity values to a parallel processor and a corresponding parallel pre-processing of the transmitted signals. Processed image rates of 5,000 Hz and more can be realized in this way. With appropriately short operating light pulses, for example short laser pulses, the sensor arrangement formed in accordance with the invention and the corresponding method are also suitable for the detection of fast-moving objects, for example on assembly lines.
In accordance with an advantageous embodiment of the invention, no storage of the light intensities incident on the sensors takes place outside the activation intervals. In this way, only the reflected light originating from the operating light pulses, including the background light incident during the period of the operating light pulses, is stored. It is generally also possible for radiation energy incident on the sensors between the activation intervals to be detected and to be evaluated, for example for the additional blanking out of the background light. Such an evaluation, however, requires additional measures to distinguish between the effective light signal during the activation intervals and the interference signals disposed outside the activation intervals.
In accordance with a further preferred embodiment of the invention, a pre-processing of the light intensity values transmitted in a previous transmission step already takes place by the parallel processor during the transmission of the light intensity values. In this way, the overall processing speed can be further increased since the pre-processing of the reception signals and the transmission of the following signals takes place simultaneously. The pre-processing can, for example, be an additional suppression of interference signals, for example of background light or a part evaluation of the signals.
Each of the signal values pre-processed by the parallel processor are preferably fed to an evaluation unit for object recognition. With a corresponding evaluation unit, not only the recognition of an object, but also, for example, the detection of its shape is possible.
The light intensities can be stored for each sensor in analog form, for example in capacitors. However, it is also possible for a digital storage of the light intensities to be carried out.
If the light intensities are stored in analog form, an analog to digital conversion of the stored values takes place preferably before the transmission of the stored values to the parallel processor, which can in particular take place for a plurality of sensors simultaneously, with this analog to digital conversion advantageously taking place for each of the sensors simultaneously whose stored light intensity values are transferred to the parallel processor in the next transmission step.
In accordance with a further advantageous embodiment of the invention, the sensors are arranged two-dimensionally in lines and/or columns next one another in each case, with the value of the light intensities respectively stored for a line or a column being transferred to the parallel processor in each transmission step. Generally, any spatially resolving arrangement of the sensors is possible, for example line-shaped, matrix- shaped, circle-shaped, in particular in concentric circles, trapezoid shaped or in any other suitable manner. A three-dimensional arrangement of the sensors can also be advantageous for certain applications.
If the sensors are arranged in line, column or matrix shape, then the analog to digital conversion preferably takes place for all sensors of one line or one column simultaneously in each case. Typical figures for a matrix shaped arrangement can be 256xc3x97256 or 512xc3x97512 sensors.
In accordance with a further advantageous embodiment of the invention, relationships are evaluated in each case between the transmitted signal values of sensors arranged next to one another in the pre-processing by the parallel processor, with preferably an edge recognition signal being generated when the difference between the output signal values of sensors arranged next to one another exceeds a pre-set threshold value. The output signal of the parallel processor already pre-processed in this way can then be evaluated in a simple manner in a desired way in an evaluation unit.
The sensors are advantageously each only activated during the activation intervals to receive the reflected operating light pulses and the sensors are in particular deactivated synchronously with the end of the respectively emitted operating light pulses. If the length of the activating interval is selected in each case such that it corresponds to the length of the operating light pulses emitted synchronously thereto, then the activation interval and the emitted operating light pulses coincide in time such that light incident on the sensors between the operating light pulses is reliably blocked out.
The receiver unit is preferably formed as a sensor chip, in particular as a CMOS based sensor chip. Unlike CCD sensors, CMOS sensors can be read in parallel and can thus be used more flexibly. An analog or digital pre-processing of the selected values by the parallel processor is possible in this way.
Further advantageous embodiments of the invention are given in the dependent claims.